My question involves real estate located in the State of: New York

I own my apartment in a co-op. I recently discovered that the management company has been inadvertently undercharging me on my monthly bill for the past two years. The error was fully theirs. Now that I've discovered the error, am I responsible for making up the accumulated difference between what they should have been charging me and what they actually billed me for? If not, should the management company have some kind of E&O coverage that would come into play in a situation like this?

Thanks!